1. Field of the Invention
This invention relates to materials handling systems, such as inventory systems for order fulfillment.
2. Description of the Related Art
Inventory of various types of items may be maintained and processed at materials handling facilities which may include, but are not limited to, one or more of: warehouses, distribution centers, cross-docking facilities, order fulfillment facilities, inventory rental facilities, packaging facilities, shipping facilities, factories, or other facilities or combinations of facilities for performing one or more functions of material (inventory) handling. For example, retailers, wholesalers, rental services, and other product distributors (which may collectively be referred to as distributors) typically maintain an inventory of various items that may be ordered by clients or customers. As another example, manufacturers may maintain an inventory of parts and/or materials for use in manufacturing processes.
FIG. 1 illustrates a broad view of the operation of an exemplary conventional materials handling facility. This Figure illustrates an exemplary order fulfillment center of a product distributor. Multiple customers 10 may submit orders 20 to the product distributor, where each order 20 specifies one or more items from inventory 30 to be shipped to the customer that submitted the order. To fulfill the customer orders 20, the one or more items specified in each order may be retrieved, or picked, from inventory 30 (which may also be referred to as stock storage) in the materials handling facility, as indicated at 40. Picked items may be delivered or conveyed, if necessary, to one or more stations in the materials handling facility for sorting 50 into their respective orders, packing 60, and finally shipping 70 to the customers 10. Note that a picked, packed and shipped order does not necessarily include all of the items ordered by the customer; a shipped order may include only a subset of the ordered items available to ship at one time from one inventory-storing location.
A materials handling facility typically also includes a receiving 80 operation for receiving shipments of stock from one or more sources (e.g., vendors) and for placing the received stock into stock storage. The receiving 80 operation may also receive and process returned purchased or rented items or orders from customers. At least some of these items are typically returned to inventory 30. Note that some items received in receiving 80 may be delivered or “cross-docked” to other locations in the material handling facility than inventory 30, for example to packing 60 or shipping 70. Further, note that the various operations of a materials handling facility may be located in one building or facility, or alternatively may be spread or subdivided across two or more buildings or facilities.
RFID Tags and RFID Readers
Radio Frequency Identification (RFID) is a method of identifying unique items using radio waves. Typically, an RFID reader communicates with an RFID tag, which holds digital information in a microchip. Note that there are chipless forms of RFID tags that use material to reflect back a portion of the radio waves beamed at them.
RFID tags generally include a microchip attached to an antenna that is packaged in a way that it can be applied to an object. The RFID tag picks up signals from and sends signals to an RFID reader. An RFID tag may contain a unique serial number, and may also include other information, which may be transmitted to the RFID reader. RFID Tags come in many forms, such as smart labels that can have a barcode printed on them, or the RFID tag may simply be mounted inside a carton or embedded in plastic. RFID tags can be active, passive or semi-passive.
Active RFID tags generally include a transmitter to send back information, rather than reflecting back a signal from the reader, as a passive tag does. Most active tags use a battery to transmit a signal to a reader. However, some tags can gather energy from other sources. Active tags can be read from 300 feet (100 meters) or more, but are typically expensive. Active RFID tags are often used for tracking expensive items over relatively long ranges.
Passive RFID tags generally do not include a battery or other embedded power supply. When radio waves from an RFID reader reach the RFID tag's antenna, the energy is converted by the antenna into electricity that can power up the microchip in the RFID tag. The RFID tag is then able to send back information stored on the chip. Simple passive tags generally cost from U.S. 20 cents to several dollars, depending on the amount of memory on the tag and other features.
Semi-passive RFID tags may be similar to active RFID tags, but the battery is used to run the microchip's circuitry but not to broadcast a signal to the RFID reader. Some semi-passive tags sleep until they are woken up by a signal from the reader, which conserves battery life. Semi-passive tags may cost a dollar or more. These tags are sometimes called battery-assisted tags.
An RFID reader is a device used to communicate with RFID tags. The reader has one or more antennas, which emit radio waves and receive signals back from the RFID tags. An RFID reader is also sometimes called an interrogator because it “interrogates” the tag.